EXTRASENSORY PERCEPTION (ESP), out-of-body experiences (OBEs), near-death experiences (NDEs), and reincarnation experiences are paranormal phenomena that rely on the abilities and memories of the experient. Another type of phenomenon places the experient in the role of observer. Ghost and UFO (unidentified flying object) sightings fall into this category, as do reports of personal encounters with such beings as aliens and fairies.

Apparitions and ghosts

Stories about ghosts have been told for centuries, and early investigators into paranormal phenomena sought to compile these stories, determine which ones seemed the most plausible, and categorize them. The Society for Psychical Research (SPR) published the first such work, including their "Census of Hallucinations," in 1894. Eventually investigators also sought to study ghosts firsthand, visiting the places where they were said to be found.

Modern researchers define a ghost as the image of a person, animal...